ON NERVOUS ENERGY 69 



genius will stimulate a vast body of men to intense 

 activity by means of a few skilfully adjusted phrases. A 

 mediocrity, on the other hand, will take all the spirit out 

 of his followers with a little verbal clumsiness. Gloomy, 

 insanitary and ill-smelling surroundings have a depress- 

 ing effect on the nervous system. A bright, cheerful and 

 pleasant environment has a very stimulating effect. 



Thus we see that this subtle force is the most reliable 

 measure of all the factors in the environment which 

 make for survival or elimination. 



The factors, then, which make for the maintenance 

 of a highly charged nervous system may be broadly 

 summarised thus : 



A complex environment leading to incessant mental 

 activity. 



A moderate amount of physical exertion. 



A plentiful diet rich in nutriment in proportion to its 

 bulk and rich in proteids. 



A rather dry, bright, bracing climate. 



Cheerful and pleasant surroundings generally. 



As these are the factors which lead to a low deathrate, 

 it follows that if the degree of fertility is to bear an inverse 

 proportion to the survival-capacity of the race, it must 

 vary inversely with these factors, and also, therefore, 

 with nervous energy. 



The principle when applied to the animal kingdom 

 will need a similar qualification to that found necessary 

 when applying it to the vegetable kingdom. Although 

 it is a necessary condition of the success of the evolu- 

 tionary scheme that a heavy deathrate should be accom- 

 panied by a heavy birthrate, yet there comes a time 

 when an increased birthrate is no longer an advantage. 

 In times of famine, for instance, it would merely add to 

 the mischief. As the principle will be adjusted to the 



